add some documentation

lib/celement.dart

@@ -1,23 +1,27 @@
 import 'package:flutter/foundation.dart';
 
+/// Country element. This is the element that contains all the information
 class CElement {
+  /// the name of the country
   String name;
+
+  /// the flag of the country
   String flag;
+
+  /// the country code (IT,AF..)
   String code;
+
+  /// the dial code (+39,+93..)
   String dialCode;
 
   CElement({this.name, this.flag, this.code, this.dialCode});
 
   @override
   String toString() {
-    return defaultTargetPlatform == TargetPlatform.android
-        ? "$flag $dialCode"
-        : dialCode;
+    return defaultTargetPlatform == TargetPlatform.android ? "$flag $dialCode" : dialCode;
   }
 
   String toLongString() {
-    return defaultTargetPlatform == TargetPlatform.android
-        ? "$flag $dialCode $name"
-        : "$dialCode $name";
+    return defaultTargetPlatform == TargetPlatform.android ? "$flag $dialCode $name" : "$dialCode $name";
   }
 }